One of the most common types of polymer blends is a blend of a homopolymer and copolymer, for example, a polyolefin homopolymer such as polypropylene and a polyolefin copolymer that consists only of olefin-derived units (ethylene, propylene, butene, etc.) or styrenic copolymers that include styrenic-derived units. Such blends are often called “impact copolymers” (“ICPs”) in the industry, and for purposes of this disclosure can include any blend of two or more polyolefins, such as blends of C2 to C8 α-olefin homopolymers and copolymers, and especially blends of polypropylene and polyethylene and/or ethylene-propylene copolymers and/or ethylene-propylene elastomers.
Olefin-based impact copolymers are of particular use in the industry and can be made from a dual-reactor process in series, or by physical blending, and/or a dual catalyst process, where in either case one component such as a rubber phase is embedded or “dispersed” in another phase such as a homopolymer polypropylene (“PP”) or “continuous” phase. The rubber can be any elastomeric copolymer (“EP”), but is preferably an ethylene-propylene copolymer. The rubber phase enhances the PP's toughness, a useful property for ICP materials. Information on its molecular weight (“MW”, including number average, weight average, z-average, molecular weight distribution, etc.) and comonomer composition (“CC”) provides an important guideline for catalyst screening, process optimization and product design. However, due to the similar MW range of the rubber and PP phases, the MWD (e.g., Mw/Mn) and CC of the polypropylene and rubber are typically convoluted with one another in conventional GPC or SEC (Gel Permeation Chromatography or Size Exclusion Chromatography) type of characterization. Thus, the MW characteristics of the rubber of ICPs cannot be directly studied without a thermal or chemical fractionation. Rubber phase separation or fractionation usually requires a lengthy and complicated procedure, and/or expensive tools.
Here, a method has been developed so that the MW characteristics of one phase of an ICP can be deconvoluted from the other phase using GPC-IR (GPC equipped with a multichannel IR detector). Another method is disclosed that allows characterization of the comonomer composition of rubber phase, together with the continuous phase or not, through a variable transformation of the GPC-IR data from MW space to CC space, which results in a quasi comonomer composition distribution (qCCD). This mathematical transformation reveals band-like features in qCCD that cannot be readily observed in the normal GPC data based on MW, therefore can be potentially used in polyolefin copolymer components analysis.